Despite the severity of the AIDS epidemic and the centrality of pregnancy and fertility to life in sub-Saharan Africa, little is known about how AIDS and its consequences alter reproductive goals and strategies. The Young Adult Families and AIDS Study (YAFAS) will collect timely and innovative data to investigate how young adults transitioning to parenthood amid a generalized epidemic simultaneously navigate the dual goals of avoiding HIV/AIDS and healthy childbearing. We situate the study in rural Malawi because counseling and testing for HIV, which are likely to influence reproduction, are just becoming available in the rural areas. An integrated longitudinal data set will include: Data from 2000 young women who will be tested for pregnancy and interviewed at quarterly intervals over a period of three years; linked data to their male sexual partners; biomarkers for HIV for both men and women, with the testing randomized in order to assess the causal influence of learning HIV serostatus; and from traditional cultural authorities to illuminate the role of local context in shaping reproductive desires. Using these new data, we address questions critical for individual, couple, national and international efforts to achieve health childbearing in a high-fertility and high HIV-prevalence setting.